"Push-pull" pushbutton switch operators are well-known in the art. It appears, however, that in the case of so-called, "emergency stop" buttons, certain regional practices have demanded rotational, or "twist-to-release", operation of the mushroon head operator to release the button after stop operation, in contrast to the conventional practice of providing a maintained contact, "push-pull" operation. That is, conventional pushbutton switch contacts are operated from their normal operating position by manually pushing a mushroom head operator inwardly in an axial direction. The contacts are maintained in such position by means of detent members acting against cam surfaces, or other means, and are released from that maintained position by an outwardly directed axial manual pull of the operator. In certain regions of the world, machine tool operating personnel use pushbuttons that are pushed inwardly to operate the contacts from a normal position, but are twisted or rotated to release the actuator and thereby return the contacts to the normal position.
In such devices, the usual biasing springs and cooperating mechanism required to provide torsional resistance have heretofore prevented installation of signal lamps which provide the operator with the usual visual indication of switch operation.